MMP Problem

[Pdelcast]

Originally Posted by What's_nitro?

I was thinking of general 6v operation- 20-30 mA is fine those small LEDs. If less resistance is needed to fix it then you'll have some brighter LEDs is all. Probably shorter lifespan, but oh well...

But don't forget about 5V will be dropped by the LEDs, leaving about 1.1V to drop across the resistor. 100 ohms would limit current to about 11ma.

[What's_nitro?]

Originally Posted by Pdelcast

But don't forget about 5V will be dropped by the LEDs, leaving about 1.1V to drop across the resistor. 100 ohms would limit current to about 11ma.

Oops, I forgot.

[BrianG]

You NEED a resistor in all cases. If you were to run, say, 2s lipo with LEDs with a Vf value of 3.2v each, the resistors are critical because the current would be 7.4v-(3.2v * 2)/0 ohms, which is mathematically infinite current.

If the LEDs are rated for 3.2v each, a string of 2 LEDs in series will require 6.4v. Running off 6v would technically be "ok" (sorta but not really), but relies on the fact that the voltage is not high enough to fully drive the LEDs and turn them into burnt silicon.

[BrianG]

Those look like high output white LEDs which I assume is for "headlights", so they need to have ~20mA or more for that use. IIRC, typical white high brightness LEDs have a Vf of a little higher than 3v. So, on 6v, they shouldn't be driven enough to technically need a resistor, but obviously something is wrong.

If anything, I'd re-wire them up so instead of 2s2p, they are 1s4p. And then use the 100-150 ohm resistor for each LED. You could use a single common resistor for all LEDs in parallel, but that's not advised.

[Pdelcast]

Originally Posted by BrianG

Those look like high output white LEDs which I assume is for "headlights", so they need to have ~20mA or more for that use. IIRC, typical white high brightness LEDs have a Vf of a little higher than 3v. So, on 6v, they shouldn't be driven enough to technically need a resistor, but obviously something is wrong.

If anything, I'd re-wire them up so instead of 2s2p, they are 1s4p. And then use the 100-150 ohm resistor for each LED. You could use a single common resistor for all LEDs in parallel, but that's not advised.

You know -- the LEDs that are on-board the MMP are driven by the BEC ... and they are 3P with 470 ohms on each.

So sounds to me like Brian's idea would be best.

[BrianG]

Originally Posted by Pdelcast

You know -- the LEDs that are on-board the MMP are driven by the BEC ... and they are 3P with 470 ohms on each.

Yeah, but that's around 7mA each. and light uniformity probably isn't a big concern. I was playing around with similar white high brightness LEDs a while back (making a 80 LED bench light) and a common resistor can get largish if enough LEDs are used in parallel at 20mA each. In this case, only 4 are used, but that still requires around 0.5w resistor. Also, when used as headlights, the brightness should be uniform for best appearance, and a common resistor didn't give good results in my playing around. I ended up making 4 strings of 20 LEDs in series and using a simple CC circuit for each chain.

By the way, I'm not trying to sound argumentative, it just might sound that way.

[Pdelcast]

Originally Posted by BrianG

Yeah, but that's around 7mA each. and light uniformity probably isn't a big concern. I was playing around with similar white high brightness LEDs a while back (making a 80 LED bench light) and a common resistor can get largish if enough LEDs are used in parallel at 20mA each. In this case, only 4 are used, but that still requires around 0.5w resistor. Also, when used as headlights, the brightness should be uniform for best appearance, and a common resistor didn't give good results in my playing around. I ended up making 4 strings of 20 LEDs in series and using a simple CC circuit for each chain.

By the way, I'm not trying to sound argumentative, it just might sound that way.

No, I wasn't suggesting a common resistor. I was agreeing with you.

[BrianG]

Originally Posted by Pdelcast

No, I wasn't suggesting a common resistor. I was agreeing with you.

lol. I saw your edit after I replied.